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The Application Of Network Camera
Dec 23, 2017

Working principle
All network camera besides conventional camera image capture function, machines also built-in digital compression controller and the operating system based on WEB, made by compressed video data encryption, through the LAN, Internet or wireless network, to the end user. TCP/IP network cameras can direct access to the digital network, therefore the system's main function is on the Internet, through the Internet or Intranet for video and audio transmission.
Composition principle
The network camera generally consists of lens, image, sound sensor, A/D converter, controller network server, external alarm, control interface, etc.
As the front part of the network camera, the lens has a fixed aperture, automatic aperture, automatic zoom, and automatic doubling, which is the same as the analog camera.
Image sensor
Image sensor has two modes: CMOS and CCD. CMOS is complementary metal oxide semiconductor CMOS silicon and germanium was mainly used these two elements are made of semiconductor, negatively charged and positively charged on the CMOS transistors to realize the basic functions. These two complementary effects generate a current that can be manipulated to record and interpret the image. The main advantage of CMOS for CCD is that it saves electricity very much. Unlike CCD and CMOS circuits composed of secondary tubes, there is little static electricity consumption. This allows CMOS to consume about a third of the power of the normal CCD, and the important problem of CMOS is that in the process of rapidly changing images, the current transformation is too frequent and too hot. The problem of dark current suppression is not great, and if the suppression is not good, it is very easy to have miscellaneous points.
The CCD image sensor is composed of two - dimensional photoelectric secondary tube and its transmission circuit in a single crystal silicon substrate. Photodiodes convert light into electric charge, and then transmute and output.
Generally, the equipment that delivers good image quality USES CCD image sensor, while the product focusing on power consumption and cost selects CMOS image sensor. But new technologies are overcoming the inherent weaknesses of each, while retaining certain features that are suitable for specific purposes. This part is the same as the analog camera. The sound sensor, or microphone, is the same as the traditional microphone.
A/D converter
The function of A/D converter is to convert analog signals such as images and sounds into digital signals. The image sensor module based on CMOS mode has direct digital signal output interface without A/D converter; And based on the pattern of the CCD image sensor module in the event of A direct digital output interface, also do not need A/D converter, but as A result of this module design, analog camera is only analog output interface, therefore the need for A/D conversion.
Image encoder
After A/D conversion, the image and sound digital signal are encoded in A certain format or standard. The purpose of coding compression is to facilitate the digitization of audio/visual signals and multimedia signals. It is easy to transmit the above signal without distortion in computer system, network and world wide web.
There are two kinds of image coding compression technology: one is hardware coding compression, and the coding compression algorithm is solidified on the chip. The other is the software coding compression based on DSP, which is the code compression of the image on DSP. Similarly, the compression of sound can be compressed by hardware encoding and software, and its coding standard is in MP3 format.
The controller is the heart of the webcam, which is responsible for the management and control of webcams. If it is a hardware compression code, the controller is an independent component; If the software code is compressed, the controller is the DSP that runs the code compression software.
Web server
Network server provides the networking of the camera, it USES the RTP/RTCP, UDP, HTTP, TCP/IP network protocol, allows the user to from their own PC using a standard browser based on the IP address of the network video camera on a visit to the network camera, watch the real-time image, and control the camera lens and yuntai.
External alarm
The network camera provides practical external interfaces for engineering applications, such as control of the 485 interface of the cloud platform, which is used for the I/O port of the alarm signal input and output. If the infrared probe finds a target and sends the alarm signal to the webcam, the network camera automatically adjusts the camera direction and real-time video; On the other hand, when a network camera detects a moving target, an alarm signal can be sent out.
Is: the basic principle of network camera image signal through the lens input and voice signal after the microphone input electrical signal is transformed by the sound of the image sensor, A/D converter converts analog signals to digital signals, then through the encoder according to certain coding compression coding standard, then under the control of the controller, by the network server according to certain network protocol on A local area network or the INTERNET, the controller can receive alarm signal and send out alarm signal, and A control signal according to the requirement.
Image coding standard
The image compression coding standards of webcams mainly include MPEG4, h.264, m-jpeg, etc.
The so-called MPEG standard refers to a series of standards for the compression and decompression of audio and video signals and multimedia signals produced by the ISO's active image expert group. By 2012, the implementation of the MPEG1, MP3, which had been completed and approved was approved. MPEG2 approved in 1994; MPEG4 and MP4 approved in 1999. Is formulating the standard has: MPEG7 and MEPG21. H. 263, h. 263 is proposed by ITU - T as h. 324 terminal using video codec advice, h. 263 after constantly improve and upgrade has more mature for many times, now most instead of h. 261, and h. 263 due to low bandwidth on transmission quality of video streaming and increasingly popular.
263 is a mixture of DPCM based on motion compensation coding, in the hybrid coding DPCM motion compensation, on the basis of motion search for motion compensation, and then using DCT transform and "of" glyph scan code, thus get the output stream. H. 263. On the basis of h.261, the search for motion vectors is increased to a semi-pixel search. At the same time, there are four advanced options such as unrestricted motion vector, grammar based arithmetic coding, advanced prediction technology and PB frame coding. Thus the aim of further reducing code rate and improving coding quality is achieved.
264 is a new digital video coding standard developed by the joint video group of the itu-t's VCEG and the ISO/IEC MPEG, which is both the itu-t's h.264 and the tenth part of the ISO/IEC MPEG4.
Under the same reconstructed image quality, h.264 can save 50% of the code rate compared with h. 263, which is about 33% better than the video format implemented by MPEG4.
M - JPEG is a sport static image compression technology, it is the movement of the video sequence is treated as continuous still images, this way of compression technology alone fully compressed, each frame in the process of editing can be stored randomly each frame, can be accurate to edit frame. However, m-jpeg only compresses the space redundancy in the frame, and the time redundancy between frames is not compressed, so the compression efficiency is not high.